Physical examination of urine
Routine urinalysis
The minimum volume needed for a routine UA usually is about 10 to 12 mL, but more is preferred. A complete UA is an assessment of the following:
- Physical properties of the urine
- Selected chemical measurements that are important for diagnosing diseases
- Microscopic contents of the urine and its sediment
Physical examination of urine: appearance
The physical examination of urine involves observations regarding the appearance of the specimen. This does not involve chemical analysis but rather observation of the characteristics of color, turbidity (cloudiness), volume, presence of foam or odor, and specific gravity.
Color
Normal urine is a shade of yellow that ranges from pale straw to yellow to amber. The color depends on the concentration of urochrome, a yellow pigment normally found in urine, and the amount of water in the specimen. A dilute specimen should be a pale straw color, and a more concentrated specimen should be a darker yellow or amber color. First morning specimens will likely be amber in color due to the concentration of the urochrome during the night. Variations in color may also be caused by diet, medication, and disease. Abnormal colors may be related to pathologic or nonpathologic factors.
Turbidity
Both normal and abnormal urine specimens may range in appearance from clear to very cloudy. Turbidity may be caused by cells, bacteria, yeast, vaginal contaminants, or crystals . It is possible for a urine specimen to be clear when voided, but as crystals form and precipitate out of the liquid, it causes the urine to become cloudy as it cools.
Possible causes of urine colors
| Color | Pathologic cause | Nonpathologic cause |
| Straw | Diabetes | Diuretics; high fluid intake (coffee, beer) |
| Amber | Dehydration | Concentrated first morning specimen; excessive sweating; low fluid intake |
| Bright yellow | — | Carotene, vitamins |
| Red | Blood, porphyrins | Menstruation, beets, drugs, dyes |
| Orange-yellow | Bile, hepatitis | Phenazopyridine (Pyridium, Uristat), dyes, drugs |
| Greenish yellow | Bile, hepatitis | Senna (laxative), cascara (laxative), rhubarb |
| Reddish brown | Old blood, methemoglobin | — |
| Brownish black | Methemoglobin, melanin | Carbidopa-levodopa (Sinemet, Parcopa) |
| Salmon pink | — | Amorphous urates |
| White (milky) | Fats, pus | Amorphous phosphates |
| Blue-green | Biliverdin, infection with Pseudomonas | Vitamin B, drugs, dyes, amitriptyline, indomethacin |
Volume
The amount of urine is rarely measured in a random specimen. With a timed specimen such as a 24-hour collection, volume is measured by pouring the complete collection into a large, graduated cylinder . It is not accurate enough to use the markings on the side of the collection container. Once the volume has been measured and recorded, a portion of the well-mixed specimen, called an aliquot, is removed for testing. The remainder is discarded or stored, depending on the preference of the laboratory.
The normal volume of urine produced every 24 hours varies according to the age of the individual. Infants and children produce smaller volumes than adults. The normal adult volume of urine produced is approximately 800 to 2000 mL in 24 hours. Excessive production of urine is called polyuria. This is common in those who have diabetes mellitus, diabetes insipidus, and certain kidney disorders. Oliguria is an insufficient production of urine, which can be caused by dehydration, decreased fluid intake, shock, renal disease, or urinary tract infections. The absence of urine production, anuria, occurs when there is renal obstruction and renal failure.
Foam
Normally the presence of foam is not recorded, but careful observation of this property can detect a significant clue to an abnormality. Foam consists of small bubbles that persist for a long time after the specimen has been swirled to mix. Foam must not be confused with any bubbles that rapidly disappear. White foam can indicate the presence of increased protein.
Greenish-yellow foam may indicate bilirubin in the urine. Care should be taken in handling such urine specimens because the greenish-yellow color may indicate that the patient has viral hepatitis, which is highly contagious. Always observe Standard Precautions and wear appropriate personal protective equipment (PPE) when handling specimens. If foam is observed and seems significant, add a note in the Comments field of a paper or electronic test report.
Odor
As with foam, odor is not normally recorded but can be an important clue to metabolic disorders. Normal urine is said to be aromatic or having a distinct smell. Changes in the odor of urine may be caused by disease, the presence of bacteria, or diet. A patient with diabetes may pass urine that has a fruity odor if he or she is excreting ketones in the urine. An ammonia or a putrid (foul or decaying) smell in the urine can be caused by an infection. An ammonia smell may also be noticed in urine that has been at room temperature for too long before it is tested. Foods such as asparagus and garlic also can produce an abnormal odor in the urine. Urine from a child with phenylketonuria (PKU) may smell “mousy.” If the odor seems significant, add a note in the Comments field of a paper or electronic test report.
Phenylketonuria
Phenylketonuria (PKU) is a rare hereditary condition in which the amino acid phenylalanine is not properly metabolized or broken down in the body. PKU that is undiagnosed or untreated can lead to severe cognitive disabilities. An accumuation of phenylalanine in the blood and urine gives body fluids the odor of wet fur.
Specific gravity
Specific gravity is defined as the weight of a substance compared with the weight of an equal volume of distilled water. In UA, specific gravity is the approximate measurement of the concentration of substances dissolved in the urine. The specific gravity of distilled water is 1.000. The normal specific gravity of urine ranges from 1.005 to 1.030, depending on the patient’s fluid intake. Most samples fall between 1.010 and 1.025. The urine’s specific gravity indicates whether the kidneys can concentrate the urine. A change in specific gravity is one of the first indications of kidney disease. Conditions such as glomerulonephritis , chronic renal insufficiency, or diabetes may lower the specific gravity. To measure specific gravity, laboratories may use a refractometer, but most use Clinical Laboratory Improvement Amendments (CLIA)-waived chemical reagent strips.
A refractometer measures the refraction (bending) of light through solids in a liquid. The result is called the refractive index, which, for our purposes, is the same as specific gravity. The refractometer requires only a drop of urine. One drop of well-mixed urine is placed under the hinged cover of the instrument. Then the value is read directly from a scale viewed through the eyepiece. The scale on the left side of the circle shows a urine-specific gravity of 1.020. The refractometer must be calibrated daily with distilled water, which should read 1.000. Note that specific gravity carries no unit of measure after the number.
The analysis that uses a reagent strip, also called a urine dipstick, is a CLIA-waived test. A reagent strip test is the most common method used for measuring specific gravity in the POL. The pad on the strip contains a chemical that is sensitive to positively charged ions , such as sodium (Na+) and potassium (K+). The pad detects the urine’s specific gravity. Various color changes indicate values between 1.000 and 1.030.